By process of elimination I doubt it was the firmware that actually caused the problem. I installed the same firmware you did and don't have the problem and due to the length of time that has passed since it was installed I would think the forum would be filled with the same type of issue of constantly running fan wen the system is cold. It's not. Try a hard boot. From power off use the volume up and power button at the same time.
Great!!
I followed the instructions below and voila!!! ... the fan is working again as it should.
Step 1: Press and hold the power button on your Surface for 30 seconds and then release it.
Step 2: Press and hold the volume-up button and the power button at the same time for at least 15 seconds and then release both.
The screen may flash the Surface logo, but continue holding the buttons down for at least 15 seconds.
Step 3: After you release the buttons, wait 10 seconds.